Beamforming radars have the ability to focus their transmission and receiver beam in a particular direction. Side to side direction is commonly referred to as the azimuth and up and down direction is commonly referred to as the elevation. Beamforming can be used to focus the beam of the radar over both azimuth and elevation. Some beamforming radars have an active electronically scanned array (AESA), which is an electronically steerable beam. The AESA allows very rapid steering of the radar beam, which is known as “beamforming”.
An AESA has many small antennas or individual antenna elements arranged in an antenna array. Each antenna element has a transmit module and a receive module. Therefore, each antenna element can individually vary the phase and magnitude of both the receive and the transmit signals. These variations, particularly in phase, provide for the beam to be steered in both azimuth and elevation. Ideally, all the antenna elements steer their individual portions of the beam in the same direction. Only when the receive signal arrives in-phase across all the antenna elements will the maximum signal be received, meaning that the antenna elements are steering the beam in the same direction. The same phase criteria are required for the transmit signal to generate the maximum transmission signal. The steering provides the ability to “aim” the main lobe of the antenna in a desired direction so that all the individual transmit and receive signals are aimed along the main lobe. The process is reciprocal, meaning that the same antenna lobe pattern will exist for both receive and transmit signals.
Each antenna element must have a delay, or phase adjustment, such that after a phase adjustment, all the antenna elements direct the beam in the same azimuth and elevation directions. If the azimuth angle and elevation angle are both zero, then all the antenna elements transmit and receive the signals simultaneously, and no phase adjustment is necessary. At non-zero angles, each antenna element has a phase adjustment to provide alignment of the wave front across the antenna array. Once the input from each antenna element is processed, each antenna input is phase-adjusted by the correct amount so that the wave front arriving from a given direction is aligned. This alignment provides for the signals transmitted by the antenna elements to also be aligned in the same direction.
Because the azimuth and elevation angles of the transmitted signals are dependent on the phase of the transmitted signals, any change in the impedances presented to the output stages of a beamforming radar can lead to variations in the directions of individual transmitted signals. Additionally, the impedance variations can lead to changes in the magnitudes of the individual transmitted signal. The variations in impedances can occur due to a variety of causes such as breaks/shorts in ball or package interfaces in IC applications or a host of other variables.